A mild, convenient and efficient single-step method for the synthesis of polysubstituted furans via ammonium ylide routes

Article abstract of DOI:10.1055/s-2004-834944

A new and convenient cyclization method for the synthesis of polysubstituted furans in a single-step via ammonium ylide routes was reported. In this process, dimethyl acetylenedicarboxylate reacted with ammonium ylide to produce polysubstituted furan in the presence of anhydrous K₂CO ₃ at room temperature. It is very economical, environmentally friendly and very easy to carry out. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2004-834944

PAPER
391
A Mild, Convenient and Efficient Single-Step Method for the Synthesis of
Polysubstituted Furans via Ammonium Ylide Routes
Method for the Synthe
i
P
n
olysubstitute
g
d Furans via
j
A
mm
o
i
nium
Y
n
lide Routes Fan,a Lina Guo,a Xueyuan Liu,a Weimin Liu,b Yongmin Liang*a,b
a
National Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. China
Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
Fax +86(931)8912582; E-mail: liangym1@hotmail.com
b
Received 14 September 2004; revised 19 October 2004
are very attractive owing to the vast range of tertiary
amines that are commercially available. In an effort to ex-
pand the scope of ammonium ylide-mediated synthesis of
cyclopropanes,7 we carried out the reaction of dimethyl
Abstract: A new and convenient cyclization method for the synthe-
sis of polysubstituted furans in a single-step via ammonium ylide
routes was reported. In this process, dimethyl acetylenedicarboxy-
late reacted with ammonium ylide to produce polysubstituted furan
in the presence of anhydrous K2CO3 at room temperature. It is very acetylenedicarboxylate (DMAD) 1 with nitrogen ylide 2a
economical, environmentally friendly and very easy to carry out.
in the presence of anhydrous K2CO3 with the intention to
obtain cyclopropene derivatives. However, reaction of 1
with 2a gave none of the expected cyclopropene deriva-
tive, but rather gave the 2,3,4-trisubstituted furan deriva-
tive 3a in 67% isolated yield at room temperature
(Scheme 1), corroborated by a single-crystal X-ray dif-
fraction structure8 (Figure 1).
Key words: substituted furans, ammonium ylide, cyclization
Substituted furans play an important role in organic chem-
istry due not only to their presence as key structural units
in many natural products and pharmaceuticals,1 but they
can also be employed as versatile synthetic intermediates
or building blocks for the preparation of a wide range of
organic compounds.2 For these reasons, the development
of new and efficient methods for the synthesis of furan de-
rivatives remains an area of current interest.3 While nu-
merous synthetic routes to polysubstituted furans have
appeared in the literature,4 mild annulation approaches
starting from commercially available materials without
transition metal catalysis is still very rare. In this paper,
we report a new and convenient cyclization method for
the synthesis of polysubstituted furans in a single-step via
ammonium ylide routes. This protocol can be used to syn-
thesize various polysubstituted furans by using different
nitrogen ylides, such as 2-substituted, 2,5-disubstituted
furan-3,4-dicarboxylates, which are key starting materials
in the synthesis of natural products containing tetrahydro-
furan rings.5 These reactions all proceeded at room tem-
perature and required no protecting groups, transition
metal catalysis or expensive materials.
Encouraged by this surprisingly successful transformation
of 1 to 3a, we tested this protocol for the synthesis of other
furan derivatives using various ammonium ylides. It was
found that the above mentioned reaction conditions were
efficient for the cyclization of acyclic substrates to pro-
duce polysubstituted furans, especially 2,3,4-trisubstitut-
ed furans, as demonstrated by entries 1–8 (Table 1). There
were difficulties in the transformations of entries 9–11 to
the corresponding furans because of the steric hindrance
arising from the proximal group.
Figure 1
Ylide research has flourished in recent years and ylides
have now become powerful and versatile synthetic tools
in organic chemistry.6 Ammonium ylide-based reactions
For the preparation of polysubstituted furans, we explored
different reaction conditions. Firstly, we used different
solvents for each reaction. We explored CH3CN, CH2Cl2,
O
H3COOC
COOCH3
Ph
N
K2CO3 (2 equiv)
+
N
H3COOC
COOCH3
+
_
Ph
CH3CN, r.t.
1 h
Br
O
1
2a
3a
Scheme 1
SYNTHESIS 2005, No. 3, pp 0391–0396
x
x
.
x
x
.2
0
0
5
Advanced online publication: 08.12.2004
DOI: 10.1055/s-2004-834944; Art ID: F13204SS
© Georg Thieme Verlag Stuttgart · New York

392
M. Fan et al.
PAPER
acetone, THF separately in every reaction of entries 1–12 byproducts. We also explored different ylides in our pro-
(Table 1) and got different yields, but the difference was cedure. We did not obtain the expected furans when we
not great in most reactions. We chose the best solvent for used triphenyl phosphine or dimethyl sulfide ylides of
each reaction and have presented in Table 1 Attempts to phenacyl bromide in our protocol. Complex products
enhance the yields and speed up the reaction by heating or were generated under identical reaction conditions.
using stronger base, such as NaOH, t-BuOK gave lower
yields of the products because of the generation of many
Table 1 Synthesis of Polysubstituted Furans Using Various Nitrogen Ylidesa
O
H3COOC
COOCH3
R2
N
+
K2CO3 (2 equiv)
solvent, r.t.
N
R1
H3COOC
COOCH3
_
+
R1
Br
O
R2
1
3
2
Entry
1
R1
R2
Solvent
CH3CN
Product
Yield (%)b
73
p-Br-Ph
H
3a
3c
3d
3e
3f
2
3
4
5
6
7
8
9
p-CH3-Ph
H
H
H
H
H
H
H
H
CH3CN
CH3CN
acetone
CH2Cl2
THF
58
52
50
66
65
54
58
21
p-CH3O-Ph
N
S
Br
S
3g
(CH3)3C
CH3CN
acetone
CH2Cl2
H3CO2C
CO2CH3
(H3C)3C
O
3h
H3CO2C
Me
CO2CH3
H3C
O
3i
Fc
3j
Synthesis 2005, No. 3, 391–396 © Thieme Stuttgart · New York

PAPER
Method for the Synthesis of Polysubstituted Furans via Ammonium Ylide Routes
393
Table 1 Synthesis of Polysubstituted Furans Using Various Nitrogen Ylidesa (continued)
O
H3COOC
R1
COOCH3
R2
N
+
K2CO3 (2 equiv)
solvent, r.t.
N
R1
H3COOC
COOCH3
_
+
Br
O
R2
1
3
2
Entry
10
R1
Ph
R2
Et
Solvent
CH2Cl2
Product
Yield (%)b
11
3k
11
Me
CO2Et
acetone
47
H3CO2C
CO2CH3
CO2Et
H3C
O
3l
a The experiments proceeded with alkyne ester (1 equiv), nitrogen ylides (1.5 equiv) and K2CO3 (2 equiv) for 1–6 h at r.t. (25 °C).
b Isolated yields.
The ammonium ylides used in these reactions are readily for the synthesis of five-membered heteroaromatic com-
accessible.7b Moreover, as DABCO can be recycled in pounds and expand the scope of ylide-based reactions as
most reactions, we envisaged a combined one-pot proce- well. Further studies are under way in our laboratory to
dure in which a catalytic amount of DABCO could be extend this general annulation strategy to the synthesis of
used. To assess the feasibility of this proposed procedure, other classes of heteroaromatic compounds from other
the use of phenacyl bromide as an in situ precursor of substrates or ylides.
ammonium ylide 2a was explored. Under the previous re-
action conditions, reaction of dimethylacetylenedicarbox-
Melting points were determined on a microscopic apparatus and are
ylate with a-bromoketone (1.5 equiv) in the presence of
anhydrous K2CO3 (2 equiv) and DABCO (cat. 20%) in an-
hydrous CH3CN produced furan 3a in 65% isolated yield.
In this modified process there is no necessity to generate
and isolate the ylide in a separate step, which, in addition
to being economical, should simplify scale-up. Some oth-
er results obtained via the modified protocol are summa-
rized in Table 2.
uncorrected. Column chromatography was carried out on silica gel.
1H NMR and 13C NMR spectra were recorded on a Varian MERCU-
RY Plus 300BB MHz spectrometer at 300 MHz (for 1H NMR) and
75 MHz (for 13C NMR) in CDCl3 using TMS as internal standard.
The FAB mass spectra were measured on a VG ZAB-HS Mass
spectrometer. A Nicolet AVATAR 360 FT-IR spectrometer was
used for IR measurements. HRMS spectra were obtained with a
Bruker APEX instrument.
Reactions of Dimethylacetylenedicarboxylate with Ammonium
Ylides to give Polysubstituted Furans; General Procedure
After the mixture of ammonium ylide (0.75 mmol) and anhyd
K2CO3 (1.0 mmol) in solvent (5 mL) was stirred for 30 min at r.t.
In conclusion, we have developed a new and efficient sin-
gle-step annulation procedure for the synthesis of
polysubstituted furans. It could provide a general strategy
Table 2 Catalytic One-Pot Synthesis of Polysubstituted Furansa
O
DABCO (20%)
K2CO3 (2 equiv)
H3COOC
COOCH3
Br
R
+
H3COOC
COOCH3
CH3CN, r.t.
R
H
O
1
3
2
Entry
R1
Ph
Solvent
Product
Yield (%)
1
2
3
CH3CN
CH3CN
CH2Cl2
3a
3b
3f
65
62
36
p-Br-Ph
S
a The experiment proceeded in 3–6 h.
Synthesis 2005, No. 3, 391–396 © Thieme Stuttgart · New York

394
M. Fan et al.
PAPER
dimethylacetylenedicarboxylate (0.5 mmol) was added. The mix-
ture was stirred at the same temperature until TLC analysis showed
complete consumption of the dimethylacetylenedicarboxylate. The
mixture was stirred the for additional 30 min. H2O (10 mL) was
added, the mixture was extracted with CH2Cl2 (3 × 15 mL), the
combined extracts were washed with water and brine and dried
(MgSO2). The solvent was evaporated under reduced pressure and
the residue was purified by flash chromatography on silica column
to give final furans (10–73%).
1H NMR (300 MHz, CDCl3): d = 2.37 (s, 3 H), 3.84 (s, 3 H), 3.90
(s, 3 H), 7.22 (d, J = 8.1 Hz, 2 H), 7.59 (d, J = 7.8 Hz, 2 H), 7.93 (s,
1 H).
13C NMR (75 MHz, CDCl3): d = 21.6, 52.2, 52.9, 113.1, 119.9,
126.2, 126.6, 129.6, 139.9, 146.2, 154.7, 162.5, 165.2.
MS: m/z (%) = 274 (100) [M+], 243 (94.1), 215 (6.12), 187 (6.04),
119 (20.63), 91 (24.47), 43 (43.33).
HRMS: m/z [M + Na] calcd for C15H14O5: 297.0733; found:
297.0735.
Catalytic One-Pot Reactions; General Procedure
DABCO (20% mmol) was added to a stirred solution of dimethyl-
acetylenedicarboxylate (1 mmol), anhyd K2CO3 (2.0 mmol) and a-
bromoketone (1.5 mmol) in anhyd solvent (5 mL) and then the mix-
ture was stirred at r.t. until TLC analysis showed complete con-
sumption of the dimethylacetylenedicarboxylate. The mixture was
stirred for additional 30 min. H2O (10 mL) was added, the mixture
was extracted with CH2Cl2 (3 × 15 mL), the combined extracts were
washed with water and brine and dried (MgSO2). The solvent was
evaporated under reduced pressure and the residue was purified by
flash chromatography on silica column to give final furans (30–
65%).
Dimethyl 2-(4-Methoxylphenyl)furan-3,4-dicarboxylate (3d)
IR (KBr): 2953, 2919, 1728, 1506, 1256, 1165, 1066, 733 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.83 (s, 3 H), 3.84 (s, 3 H), 3.89
(s, 3 H), 6.92–6.95 (d, J = 8.4 Hz, 2 H), 7.65–7.68 (d, J = 8.7 Hz, 2
H), 7.91 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 52.1, 52.8, 55.5, 112.3, 114.3,
120.0, 121.6, 128.4, 145.9, 155.0, 1160.8, 162.6, 165.1.
MS: m/z (%) = 290 (100) [M+], 259 (58.97), 135 (21.06), 57 (12.74),
43 (15.09).
HRMS: m/z [M + Na] calcd for C15H14O6: 313.0683; found:
313.0688.
Preparation of Ammonium Ylides (as Exemplified by the Pro-
cedure of Ammonium Ylide 2a); General Procedure
Dimethyl 2-Pyridylfuran-3,4-dicarboxylate (3e)
Mp 116–118 °C.
IR (KBr): 2923, 1730, 1620, 1544, 1460, 1066, 793 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.86 (s, 3 H), 3.97 (s, 3 H), 7.20–
7.24 (m, 1 H), 7.69–7.77 (m, 2 H), 8.02 (s, 1 H), 8.59 (d, J = 4.5 Hz,
1 H).
13C NMR (75 MHz, CDCl3): d = 52.3, 53.1, 116.6, 119.9, 123.5,
136.9, 147.3, 147.6, 150.2, 151.9, 162.2, 165.3.
DABCO (10 mmol, 1.12 g) was added to a stirred solution of phen-
acyl bromide (10 mmol, 3.10 g) in THF (50 mL). The reaction was
stirred at r.t. for 30 min. THF was removed under reduced pressure
and the resulting solid was washed with petroleum ether (40–60).
The solid was then dissolved in a mixture of MeOH–C6H6 (1:1; 5
mL each). The solvent mixture was removed under reduced pres-
sure to afford ammonium ylide 2a as a white solid (4 g, 95%).
Dimethyl 2-Phenylfuran-3,4-dicarboxylate (3a)8
MS: m/z (%) = 261 (50) [M+], 230 (100), 78 (28), 57 (32), 43 (24).
Mp 68–70 °C.
IR (KBr): 3151, 2955, 1717, 1552, 1441, 1282, 1151, 771, 693
cm–1.
1H NMR (300 MHz, CDCl3): d = 3.86 (s, 3 H), 3.92 (s, 3 H), 7.40–
7.43 (m, 3 H), 7.69–7.72 (m, 2 H), 7.97 (d, J = 3 Hz, 1 H).
13C NMR (75 MHz, CDCl3): d = 52.2, 53.0, 113.8, 120.0, 126.6,
129.0, 129.7, 146.5, 154.3, 162.5, 165.1.
HRMS: m/z [M + Na] calcd for C13H11NO5: 284.0529; found:
284.0530.
Dimethyl 2-Thiopenylfuran-3,4-dicarboxylate (3f)
Mp 46–48 °C.
IR (KBr): 3106, 2921, 1723, 1554, 1441, 1279, 1066, 707 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.88 (s, 3 H), 3.95 (s, 3 H), 7.11
(dd, J = 4.2, 4.8 Hz, 1 H), 7.44 (d, J = 5.1 Hz, 1 H), 7.68 (d, J = 3.6
Hz, 1 H), 7.89 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 23.0, 30.0, 52.3, 52.7, 112.0, 120.0,
128.0, 128.2, 130.4, 146.0, 151.6, 162.4, 164.0.
MS: m/z (%) = 260 (70.80) [M+], 229 (100), 105 (16.89), 77 (26.31).
HRMS: m/z [M + Na] calcd for C14H12O5: 283.0577; found:
283.0583.
Dimethyl 2-(4-Bromophenyl)furan-3,4-dicarboxylate (3b)
MS: m/z (%) = 266 (50) [M+], 235 (76.13), 111 (13.45), 83 (4.32).
Mp 79–81 °C.
IR (KBr): 3163, 2951, 1733, 1547, 1487, 1325, 1167, 1059, 816
cm–1.
1H NMR (300 MHz, CDCl3): d = 3.85 (s, 3 H), 3.91 (s, 3 H), 7.56
(dd, J = 8.7, 9.0 Hz, 4 H), 7.96 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 52.3, 53.0, 114.2, 120.2, 124.1,
127.8, 128.2, 132.2, 146.7, 153.4, 162.3, 164.8.
HRMS: m/z [M + Na] calcd for C12H10O5S: 289.0141; found:
289.0147.
Dimethyl 2-(4-Bromothiopenyl)furan-3,4-dicarboxylate (3g)
Mp 68–70 °C.
IR (KBr): 2951, 1728, 1556, 1443, 1277, 1068, 812, 762 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.86 (s, 3 H), 3.92 (s, 3 H), 7.06
(d, J = 3.9 Hz, 1 H), 7.44 (d, J = 3.9 Hz, 1 H), 7.86 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 52.0, 52.4, 111.7, 116.0, 120.0,
128.2, 130.3, 131.4, 145.7, 150.7, 161.9, 163.4.
MS: m/z (%) = 338 (100) [M+], 340 (93.87), 307 (85.46), 309
(80.56), 183 (19.42), 185 (19.98), 155 (13.95), 157 (13.72), 113
(43.45), 59 (25.64).
HRMS: m/z [M + Na] calcd for C14H11BrO5: 360.9682; found:
MS: m/z (%) = 344 (5.48) [M+], 346 (5.69), 313 (7.92), 315 (8.07),
360.9677.
265 (100), 250 (27.85), 191 (6.63), 59 (6.62), 45 (7.92).
Dimethyl 2-(4-Methylphenyl)furan-3,4-dicarboxylate (3c)
Mp 95–97 °C.
HRMS: m/z [M + H] calcd for C12H9BrO5S: 344.9427; found:
344.9434.
IR (KBr): 3158, 2954, 1723, 1508, 1441, 1328, 1162, 1060, 821
cm–1.
Synthesis 2005, No. 3, 391–396 © Thieme Stuttgart · New York

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Method for the Synthesis of Polysubstituted Furans via Ammonium Ylide Routes
395
Dimethyl 2-(tert-Butyl)furan-3,4-dicarboxylate (3h)
IR (KBr): 3153, 2956, 1732, 1555, 1439, 1392, 1367, 1281, 1154,
1066, 767 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.32 (s, 9 H), 3.80 (s, 3 H), 3.89
(s, 3 H), 7.81 (s, 1 H).
Acknowledgment
The authors thank the NSF-20021001, NSF-20172024 and the
‘Hundred Scientist Program’ from the Chinese Academy of Sci-
ences for the financial support of this work.
13C NMR (75 MHz, CDCl3): d = 28.7, 34.3, 51.9, 52.7, 112.4, 118.5,
145.1, 162.4, 162.7, 166.1.
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MS: m/z (%) = 240 (7.14) [M+], 225 (20.52), 209 (12.46), 193 (100).
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263.0886.
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IR (KBr): 3150, 2953, 2922, 1720, 1556, 1442, 1304, 1088, 759
cm–1.
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(s, 3 H), 7.72 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 13.7, 52.1, 113.0, 118.9, 145.8,
159.6, 162.8, 163.8.
MS: m/z (%) = 198 (3.58) [M+], 166 (16.72), 167 (11.34), 137
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HRMS: m/z [M + Na] calcd for C9H10O5: 221.0420; found:
221.0425.
Dimethyl 2-Ferrocenylfuran-3,4-dicarboxylate (3j)
Mp 61–63 °C.
IR (KBr): 3147, 3089, 2952, 1727, 1557, 1466, 1278, 1065, 815
cm–1.
1H NMR (300 MHz, CDCl3): d = 3.83 (s, 3 H), 3.92 (s, 3 H), 4.13
(s, 5 H), 4.36 (s, 2 H), 4.83 (s, 2 H), 7.83 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 52.2, 52.4, 67.8, 69.9, 70.0, 72.7,
111.2, 119.8, 145.3, 157.3, 162.7, 164.7.
FAB–MS: m/z (%) = 369 (100) [M+ + 1], 338 (22), 304 (13).
HRMS: m/z [M + H] calcd for C18H16FeO5: 369.0420; found:
369.0418.
Dimethyl 2-Ethyl-5-phenylfuran-3,4-dicarboxylate (3k)
IR (KBr): 2921, 1725, 1563, 1440, 1215, 1068, 765, 693 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.32 (t, J = 7.5 Hz, 3 H), 3.03 (q,
J = 7.5 Hz, 2 H), 3.84 (s, 3 H), 3.90 (s, 3 H), 7.40 (q, J = 7.5 Hz, 3
H), 7.67 (d, J = 7.5 Hz, 2 H).
13C NMR (75 MHz, CDCl3): d = 12.5, 21.4, 52.1, 52.9, 113.6, 114.7,
126.2, 128.9, 129.2, 131.2, 150.7, 162.9, 163.6, 165.8.
MS: m/z (%) = 288 (50.10) [M+], 273 (15.87), 256 (98.27), 257
(57.10), 170 (92.31), 105 (100), 77 (81.70).
(5) Pei, W.-P.; Pei, J.; Li, S.-H.; Ye, X.-L. Synthesis 2000, 2069.
(6) (a) Li, A.-H.; Dai, L.-X.; Aggarwal, V. K. Chem. Rev. 1997,
97, 2341. (b) Hanessian, S.; Andreotti, D.; Gomtsyan, A. J.
Am. Chem. Soc. 1995, 117, 10393. (c) Ye, S.; Huang, Z.-Z.;
Xia, C.-A.; Tang, Y.; Dai, L.-X. J. Am. Chem. Soc. 2002,
124, 2432. (d) Aggarwal, V. K.; Thompson, A.; Jones, R. V.
H. Chem. Commun. 1997, 1785. (e) Solladié-Cavallo, A.;
Diep-Vohuule, A.; Isarno, T. Angew. Chem. Int. Ed. 1998,
37, 1689; Angew. Chem. 1998, 110, 1824. (f) Aggarwal, V.
K.; Alonso, E.; Fang, G.; Ferrara, M.; Hynd, G.; Porcelloni,
M. Angew. Chem. Int. Ed. 2001, 40, 1433; Angew. Chem.
2001, 113, 1482.
HRMS: m/z [M + Na] calcd for C16H16O5: 311.0890; found:
311.0888.
Dimethyl 2-Methyl-5-carbethoxyfuran-3,4-dicarboxylate (3l)
IR (KBr): 2955, 2255, 1725, 909, 733 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.33 (t, J = 7.2 Hz, 3 H), 2.64 (s,
3 H), 3.82 (s, 3 H), 3.92 (s, 3 H), 4.33 (q, J = 7.2 Hz, 2 H).
13C NMR (75 MHz, CDCl3): d = 14.3, 52.3, 53.2, 61.9, 114.2, 157.4,
162.3, 162.5, 163.9.
MS: m/z (%) = 270 (18.3) [M+], 239 (41.7), 238 (100), 211 (29.7),
210 (53.6), 179 (65), 178 (48.8), 43 (51.9).
(7) (a) Dai, L.-X.; Hou, X.-L.; Zhou, Y.-G. Pure Appl. Chem.
1999, 71, 369. (b) Papageorgiou, C. D.; Ley, S. V.; Gaunt,
M. J. Angew. Chem. Int. Ed. 2003, 42, 828.
HRMS: m/z [M + Na] calcd for C12H14O7: 293.0632; found:
293.0636.
(8) Crystal data for 3a: CCDC 249973. C14H12O5, mp: 68–70
°C; chemical formula weight: 260.24, monoclinic space
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PAPER
least-squares on F2: Goodness-of-fit on F2 1.073: Final R
indices [I > 2d (I)] R1 = 0.0383, wR2 = 0.1038, R indices (all
data) R1 = 0.0524, wR2 = 0.0138. Extinction coefficient
0.126 (7), Largest diff. peak and hole 0.173 Å–3 and –0.163e
Å–3.
group P2 (1)/c, a = 14.698 (2), b = 11.720 (1), c = 7.3105 (7)
Å; a = 90.00°, b = 97.92 (9)°, g = 90.00°, U = 1247.3 (2) Å3.
T = 290 (2) K, Z = 4, DC = 1.386 Mg/M3, m = 0.106 mm–1,
l = 0.71073 Å, F(000) 544, Crystal size 0.52 × 0.48 × 0.48
mm3, 2255 independent reflections [R(int) = 0.0122],
Reflections collected 2690: Refinement method, full-matrix
Synthesis 2005, No. 3, 391–396 © Thieme Stuttgart · New York